Marks of the Anthropocene: 7 signs we have made our own epoch

Even if humanity is long gone in tens of millions of years, there will still be a clear sign of us and the way we lived left preserved in our planet’s geological record.

There is now overwhelming evidence that our impact on Earth constitutes its own distinct geological epoch, dating from the middle of the 20th century. Here are the seven signs that will clearly identify the Anthropocene epoch for future geologists.

1. Nuclear weapons

Our war efforts have left their mark on geology. When the first nuclear weapon was detonated on 16 July 1945 in New Mexico, it deposited radionuclides – atoms with excess nuclear energy – across a wide area. Since 1952, more explosive thermonuclear weapons have been tested, leaving a global signature of isotopes such as carbon-14 and plutonium-239.

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2. Fossil fuels

The products of burning fossil fuels will also be an obvious giveaway of the Anthropocene. Current rates of carbon emission are thought to be higher than at any time in the last 65 million years. The concentration of carbon dioxide in the atmosphere has risen sharply since 1850 and now exceeds 400 parts per million, which will be recorded in any Antarctic ice cores that manage to survive global warming. Burning fossil fuels has also increased the ratio of carbon-12 to carbon-13 isotopes, which will be detectable in tree rings, limestone, and fossilised bones and shells. Our fuel consumption also spreads small, unburned particles of carbon in the air, which can become captured in sediments and glacial ice.

3. New materials

One of the biggest signs of our time will be the presence of three things we use every day: concrete, plastics and aluminium. Aluminium in its elemental form was unknown before the 19th century, but we have now produced around 500 million tonnes of it. Concrete has been around for longer – it was invented by the Romans – but in the 20th century it became our most widely used building material. We have now produced about 50 billion tonnes of the stuff – enough to spread a kilogram on every square metre of Earth – and more than half of that was made in the last 20 years. Plastics, initially developed in the 1900s, have grown rapidly since the 1950s, and we now produce 500 million tonnes a year. Sediments containing any of these materials will be a clear sign of the Anthropocene.

4. Changed geology

Every time we destroy a patch of rainforest, this changes the future of Earth’s geology. So far, we have transformed more than 50 per cent of Earth’s land area for our own purposes. Deforestation, farming, drilling, mining, landfills, dam-building and coastal reclamation are all having widespread effects on sedimentary processes, disrupting how layers of rock are laid down, which will be detectable thousands of years in the future.

5. Fertilisers

Our attempts to feed a burgeoning population will leave clear indicators, too. Levels of nitrogen and phosphorus in soils have doubled in the last century because of our increased use of fertilisers. We produce 23.5 million tonnes of phosphorus a year, twice the rate seen during the previous epoch, the Holocene. Human activity has had perhaps the biggest impact on the nitrogen cycle for 2.5 billion years, increasing the amount of reactive nitrogen by 120 per cent compared to the Holocene.

6. Global warming

Anthropogenic climate change will be easily distinguishable in the future. Last century, Earth’s temperature rose by between 0.6 and 0.9 °C, more than the amount of natural variability seen in the Holocene, which has been calculated based on the oxygen isotopes in Greenland’s ice cores. Average global sea levels are higher than at any point in the past 115,000 years and are rising rapidly, which may also be detectable in future.

7. Mass extinction

For as long as life has existed, organisms have gone extinct, but mass extinctions sparked by massive global changes mark the end and beginning of several geological periods. Some estimates predict that we are on our way to the sixth mass extinction event in Earth’s history, with three-quarters of species set to be wiped out in the coming centuries. Palaeontologists of the future will notice the sudden disappearance of many species from the fossil record as the Anthropocene gets under way.